1. Field of the Invention
The present invention relates to a suspension apparatus for a vehicle (hereinafter referred to as a “vehicle suspension apparatus”), and more particularly to a vehicle suspension apparatus which can control stiffness of a stabilizer bar.
2. Description of the Related Art
Japanese Patent Application Laid-Open (kokai) No. H7-257143 disclose a conventional vehicle suspension apparatus of such a type in which one of arm portions of a stabilizer bar is connected to a piston rod of an oil-hydraulic cylinder via a lever. In the vehicle suspension apparatus disclosed in the publication, one arm portion of the stabilizer bar to which the lever is connected is assembled to a frame, which is a portion of the vehicle body, via the oil-hydraulic cylinder; the other arm portion is assembled to the frame via a stabilizer link; and a torsion bar portion between the arm portions is assembled to an axle. The cylinder body of the oil-hydraulic cylinder is assembled to the frame, and the lever is assembled to the frame via a rotation fulcrum provided at an intermediate portion of the lever.
In the vehicle suspension apparatus disclosed in the publication, when the left and right wheels move vertically in the same direction (in the same phase) with extension and contraction of the oil-hydraulic cylinder being prohibited, the stabilizer bar is not twisted. When the left and right wheels move vertically in opposite directions (in opposite phases) with extension and contraction of the oil-hydraulic cylinder being prohibited, the stabilizer bar is twisted.
Meanwhile, when the left and right wheels move vertically in the same phase with extension and contraction of the oil-hydraulic cylinder being permitted, as in the case where extension and contraction of the oil-hydraulic cylinder are prohibited, the stabilizer bar is not twisted. When the left and right wheels move vertically in opposite phases with extension and contraction of the oil-hydraulic cylinder being permitted, unlike the case where extension and contraction of the oil-hydraulic cylinder are prohibited, the stabilizer bar is not twisted because of extension and contraction of the oil-hydraulic cylinder.
Incidentally, in the vehicle suspension apparatus disclosed in the publication, the stroke of the piston rod in the state in which the oil-hydraulic cylinder can extend and contract can be made smaller than that of the corresponding arm portion, by properly setting the rotation fulcrum of the lever. This configuration reduces the size of the oil-hydraulic cylinder and the space occupied thereby. However, in the case where the rotation fulcrum of the lever is set as described above, when the oil-hydraulic cylinder cannot extend and contract, the force acting on the piston rod increases in accordance with the lever ratio, whereby excessively large load is imposed on the frame to which the oil-hydraulic cylinder is assembled.